The ECE approves more measuring apparatuses

The way is paved for four FAIR components

The CBM experiment’s superconducting dipole magnet (dark blue) together with the muon detector system. The detector layers (light blue and purple) are shielded by iron plates (green). The particles are produced in a target located in front of the magnet, deflected by the magnetic field and then fly into the muon detector system. (Image courtesy of CBM collaboration)

In the first half of 2015, FAIR GmbH’s Expert Committee Experiments (ECE) has approved the Technical Design Reports of four measuring apparatuses for the future FAIR facility. These include three detectors in the Compressed Baryonic Matter (CBM) experiment and a system for acquiring data and controlling the plasma physics experiments of the HEDgeHOB collaboration, part of the Atomic, Plasma Physics and Applications (APPA) experimental alliance.


The aim of the CBM experiment is for scientists to gain insights into extreme states of matter, such as those that exist today in compact stellar objects like neutron stars. Researchers assume that such unimaginably high levels of density exist at the centre of a neutron star that the normal building blocks of atomic nuclei – protons and neutrons – dissolve into their component parts to form a plasma of quarks and gluons. A similar elementary state of matter would have prevailed in space for fractions of a second following the Big Bang. Collisions between high-energy atomic nuclei can be used to generate and analyse such highly compressed nuclear matter in accelerator-based experiments.


With the Muon Chamber (MUCH) detector, scientists have developed a system that can detect extremely lightweight particles known as muons. These elementary particles are produced when heavier particles disintegrate inside the compressed reaction zone, and can thus provide information on the state of the matter. Muons are particularly well suited for use as diagnostic probes because they only react very weakly with matter and can therefore easily exit the reaction zone. On the other hand, the property of being able to penetrate material without being stopped makes muons very difficult to detect. The MUCH detector system is therefore made up of several layers of tracking chambers located between thick iron plates. These iron plates filter out all heavy particles; only the muons are able to penetrate all the iron plates and reach the final detector layer.


“Spectators” provide information on the collision
Another CMB detector, the Projectile Spectator Detector (PSD), measures the beam of projectile fragments that are not directly involved in the reaction. In the experiment, nuclei composed of many protons and neutrons are fired at one another at very high speed (energy) inside what is known as the target. If the two nuclei collide centrally, all protons and neutrons contained in both nuclei are involved in the collision (participants). However, if the two nuclei collide peripherally, only the protons and neutrons contained in the area of impact are involved in the collision; the rest are only slightly deflected and continue their flight (spectators). So measuring these spectators allows researchers to determine the centrality of the collision and consequently the number of participants. The more central the collision, the larger the reaction zone, and the higher the density and temperature of the fireballs that are created. The PSD provides all this information by measuring the projectile spectators – i.e. the protons and neutrons of the projectile nuclei that were not directly involved in the collision.


Detecting particles
The Time of Flight (TOF) detector in the CBM experiment measures the length of time it takes a particle to fly from one detector to the next. Given that the researchers know the exact distance between the detectors, the speed of the particle can be calculated directly from its flight time. Taking this speed and the particle’s momentum as measured in the magnetic field, the particle mass and therefore particle type can be determined. In contrast to the RICH detector, which measures the speed of particles travelling at velocities close to the speed of light (see also: FAIR news from 6 March 2015), the TOF detector can also measure slower speeds. Both detectors complement one another, making it possible to identify particles travelling at a wide range of speeds. This allows scientists to not only determine how many or what types of particles are generated in the collision, but also discover new particles and draw conclusions about the composition of extremely dense and hot nuclear matter.


Data acquisition and synchronisation of experiment and accelerator
FAIR’s experiments in plasma physics study matter under extreme conditions (temperatures over 10,000 degrees Celsius and pressures greater than one million atmospheres) to better understand phenomena such as the interior of gas giants like Jupiter. To perform these experiments successfully, it is essential to synchronise all diagnostic systems to the accelerator and store the data quickly, as this enables the experiment to record new data within minutes. This is the task of SCADA (Supervisory Control and Data Acquisition) of the HEDgeHOB collaboration, which ensures both synchronisation of local devices with the accelerator and automated processing of the experimental data.


The TDRs were drafted by scientists involved in the FAIR experiment collaborations and reviewed positively by the Expert Committee Experiments – a board of internationally recognised scientists. The experiment collaborations can now apply for funding from FAIR partner countries and, if required, third-party funding to enable them to start constructing the measuring apparatuses.

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